The performance of an antenna used for the reception and/or transmission of electromagnetic signals is influenced by, inter alia, the immediate environment surrounding the antenna, due to electromagnetic interaction between the antenna and objects proximate to the antenna. The antenna-object interaction can manifest itself in undesirable ways, for example in the form of high return loss, decreased radiation efficiency, and radiation pattern perturbations. By designing the antenna arrangement in a proper way, taking into account the influence of the surrounding environment, it is possible to tune the performance of the antenna for the specific environment in which the antenna is used.
Antennas which are used in devices or terminals such as, for example, cell phones or portable computers, are however, exposed to a changing environment, such as, for example, the configuration of a “clam shell” cellular phone, or the body/lid configuration in the case of a portable “notebook” computer. In such changing environments, an antenna cannot be tuned once and for all for optimal performance. Instead, there is a need for solutions which can adaptively tune the antenna's performance depending on the situation, since there is no single tuning that maximizes the antenna's, and the corresponding communications system's performance for all possible environments.
A solution which may adapt an antenna or an antenna arrangement to a number of environment scenarios can offer good antenna performance for terminals used for mobile communications, due to the nature of usage of such devices. In particular, notebook (“laptop”) computers are typically used in one of only three basic ways:                lid open, i.e., notebook display visible and keyboard available;        lid closed, i.e., notebook display not visible;        lid closed (or non-existent), and display facing away from the computer chassis, such as in a computer using a “touch screen user interface”.        
The second of these is typical of the stationary scenario, when a computer is connected to a “docking station” or “port replicator”, whereas the first and third are typical of an “unconnected scenario”. When the main influence on the antenna performance is the laptop computer configuration, i.e., the lid position in relation to the computer chassis, as is almost always the case, an adaptive solution to a variable environment can be limited to handle a finite set of scenarios, in this case two. This allows for a low-complexity, low-cost solution, for example implemented as configuration-based signal routing using switched networks.
A communications system in which an antenna or antenna arrangement is installed will only achieve the desired performance level if the antenna performance, for example in terms of efficiency, pattern correlation (in the case of multiple antennas and for a given propagation channel), or directionality (radiation pattern spatial selectivity), is maintained. Since the antenna performance will be highly affected by the installation scenario, it is crucial to account for the properties of the platform (notebook, PDA, handset, etc.) when choosing the antenna solution. Some platforms, such as notebook computers with lids and clamshell phones, have inherently variable form factors, i.e. physical shapes, which makes choosing an antenna solution difficult. Different modes of operation (for example ‘lid open’ or ‘lid closed’) may require significantly different antenna solutions in order to provide good antenna performance.
Most existing antenna designs for portable devices ignore the problem of a variable form factor in the portable device. One and the same antenna(s) is/are used, regardless of the current configuration of the device in which the antenna(s) is/are installed, in addition to which the antennas are designed for a certain mode of operation, or are designed to provide an average performance quality which allows the device in which the antenna is installed to operate with an acceptable degree of performance for all form factors of the device. Thus, the antenna performance, and hence the corresponding communications system's performance, will never be ideal for all scenarios.
There are known solutions which do account for different form factors, and which are based on tuning the antenna performance based on some sort of quality measurement. One example of such a solution is shown in US patent application 2004/0027300 A1, Young-Eil Kim et al.
The solution disclosed in US 2004/0027300 A1 teaches the use of a switch installed in a laptop computer, by means of which it is possible to sense if the lid of the laptop is open or closed, and to switch between different antennas based on this.
It would be desirable to improve the solution shown in US 2004/0027300 A1, so that an increased tuneability and thereby improved antenna and communications system performance can be obtained.